1. Field of the Invention
This invention has relation to air volume control dampers installed in cylindrical ducts.
2. Description of the Prior Art
Customarily an air volume control damper is used for reducing flow volume in a duct, not positive shutoff. For many years such air volume control dampers have been pivotally mounted in ducts and each has then been fixedly positioned to adjust by reducing the volume of air flow in its duct to balance that flow with respect to the flow through other ducts in a particular forced air or warm air heating system.
In heating, ventilating and air conditioning systems using a network of ducts to distribute air from a central source to various separated locations, the optimum location of the air volume control dampers along such ducts cannot be easily determined in advance of actual installation. For that reason, the dampers must be so structured that they can be installed in the ducts in the field after the ducts have been formed. This ability to be field installed to pivot on axes normal to the longitudinal axes of ducts having cylindrical sheet metal walls is a prerequisite of substantially all of the prior art structures discussed below.
It is known to mount a flat circular damper plate or blade in a cylindrical duct by attaching damper clips on diametrically opposite sides of the damper blade and by extending threaded pivot pins outwardly from those clips through the side walls of the duct. Such a damper was adjusted to a proper angle in the duct so as to get the desired amount of air flow through it. It was then fixedly positioned with respect to the duct by turning butterfly nuts down on the threaded pivot pins to clamp the inner face of the duct up against the damper clips. See U.S. Pat. No. 2,134,844 granted to Schartow in November of 1938; and U.S. Pat. No. 1,458,144 granted to Olinger in June of 1923.
It is known to deform draft control damper shutters to provide reinforcing and stiffening ribs. See U.S. Pat. No. 2,309,425 granted to Weyenberg in January of 1943; U.S. Pat. No. 2,124,484 granted to Corbman et al. in July of 1938; and U.S. Pat. No. 1,972,677 granted to Bornheim in September of 1934.
It is known to form pivot members which are integral with cast iron or steel damper blades. See U.S. Pat. No. 901,485 granted to Schafer in October of 1908; and U.S. Pat. No. 980,011 granted to Schafer in December of 1910.
Other patents which were cited as pertinent in a search of the prior art, and which appear to be of general interest in relation to the present invention are:
______________________________________ U.S. Pat. No. Patentee Granted ______________________________________ 249,303 Clark November 1881 403,489 Schofield May 1889 794,534 Meyers July 1905 1,398,038 Olinger November 1921 1,480,949 Olinger January 1924 2,433,749 Field, Jr. December 1947 3,007,673 Paxton et al. November 1961 ______________________________________
Before the present invention, in order to obtain precision, it has been customary to cut out damper blades using a circular shear. This was a labor intensive and time consuming practice where production of relatively large numbers of dampers were required.
What was needed before the present invention was a circular damper which was inexpensively made, but precision made to be easily fitted into a cylindrical duct and to be pivoted on diametrically opposite sides thereof in the duct. Such a damper should not vibrate in the duct regardless of its positioning and regardless of the velocity of the air flow through the duct. It should be producable in substantial quantities at extremely low prices. The damper of the present invention fulfills these objectives.